Change the informational redo log format tag to say "MariaDB 10.2.3"

MariaDB 10.2 incorporates MySQL 5.7. MySQL 5.7.9 introduced an informational field to the InnoDB redo log header, which identifies the creating server version, in
WL#8845: InnoDB: Redo log format version identifier
The informational message would be displayed to the user, for example if someone tries to start up MySQL 8.0 after killing a MariaDB 10.2 server.
In the current MariaDB 10.2 source code, the identifier string would misleadingly say "MySQL". We should change it to "MariaDB". We should also make sure that the correct version number is being written.
This would probably involve changing a single line in the file log0log.h:

#define LOG_HEADER_CREATOR_CURRENT	"MySQL " INNODB_VERSION_STR

This is only a cosmetic change. The compatibility check is based on a numeric identifier. We do not need to change that identifier as long as we are not changing the way how redo log records are being interpreted in crash recovery. So, MariaDB 10.2.3 and later would use a redo log format that is compatible with MySQL 5.7.x with x>=9.